The electronics industry employs gases, such as nitrogen, in manufacturing operations, such as in the manufacture of very large scale integrated circuits. Increasingly the cleanliness or purity requirements of such gases are becoming more stringent. In particular, the particulate content of such gases is critical to the quality of the product produced by such manufacturing operations.
In order to maintain good quality control over the manufacturing process, the particulate content of the gas must be monitored and measured. Since the gas is supplied to the manufacturing operation at an elevated pressure and since the particulate measuring equipment generally operates at about atmospheric pressure, the pressure of the gas sample must be reduced, often by a factor of ten or more, prior to passage to a particulate counter. This pressure reduction is generally done through a valve or critical orifice usually containing moving or rubbing parts. This causes the generation of significant quantities of particulates thus reducing the accuracy of the measurement. Since the particulate content of the gas is of the order of only a few particles per cubic foot, it can be seen that even minor particulate generation due to the sampling device would have a detrimental effect on the accuracy of the particulate measurement.
Moreover, conventional gas sampling devices generally contain bends or other potential for dead spaces which trap and remove particles from the sample gas, thus further compromising the integrity of the particulate measurement.
In addition, with conventional sample collection systems, the product gas flow must be stopped and the product line depressurized to allow the sample collection device to be connected. This not only causes production delays but also exposes the product gas line to contamination from the outside atmosphere.
Accordingly, it is an object of this invention to provide a gas sampling device which can be inserted into a gas process stream without disturbing the operation of the gas supply or causing contamination of the gas supply system.
It is another object of this invention to provide a gas sampling device which can reduce the pressure of a gas sample without altering the particulate content of the sample.